A disk drive is a digital data storage device that stores information on concentric tracks on a storage disk. The storage disk is coated on one or both of its primary surfaces with a magnetic material that is capable of changing its magnetic orientation in response to an applied magnetic field. During operation of a disk drive, the disk is rotated about a central axis at a constant rate. To read data from or write data to the disk, a head is positioned adjacent to a desired track of the disk while the disk is spinning.
Writing is performed by delivering a polarity-switching write current signal to the head while the transducer is positioned adjacent to the desired track. The write signal creates a variable magnetic field at a gap portion of the magnetic transducer that induces magnetically polarized transitions on the desired track. The magnetically polarized transitions are representative of the data being stored.
Reading is performed by sensing the magnetically polarized transitions on the disk surface. As the disk spins adjacent to the head, the magnetically polarized transitions on the disk surface induce a varying magnetic field in the head. The head converts the varying magnetic field into a read signal that is delivered to a preamplifier and then to a read channel for appropriate processing. The read channel converts the read signal into a digital signal that is processed and then provided by a controller to a host computer system.
The reading and writing functions of the head are performed by separate elements. The term “head” thus typically includes both a standard thin-film write element and an MR read element. The present invention relates to the MR read element portion of the head.
An MR read element is formed by a conductive read material that changes its resistance in the presence of a magnetic field. As the disk moves relative to the head, the magnetically polarized transitions on the disk cause the resistance of the conductive read material to change. These changes in resistance correspond to the data stored on the disk.
To allow the changes in resistance of the MR read element to be detected, the voltage across (or the current flowing through) the read element is held constant, and the current flowing through (or the voltage across) the read element is measured. Typically (i.e., when the MR read element is operating in its linear range), if either the current or voltage is held constant, the other of the current or voltage will vary in a linear relationship with changes in resistance. Changes in resistance can thus be detected based on the varying parameter. Typically, a bias current applied to the MR element is held constant, and the voltage across the MR element is monitored to detect changes in resistance indicative of changes in magnetically polarized transitions on the disk.
A modern disk drive can be configured to operate even though certain components are not error free. For example, imperfections on the disk surface that interfere with data storage and recovery can be masked by error correction schemes and/or by mapping out failed portions of the disk surface. However, proper operation of the MR read element is important to proper operation of the entire hard disk drive. Stated conversely, if the MR read element fails or the operation thereof is significantly degraded, the entire hard disk drive may become unable to perform as desired or expected.
A number of factors are known to contribute to the failure of the MR read element of a hard disk drive. One such factor is the magnitude of the bias current applied to the MR read element. Over the life of the MR read element, the bias current causes a degradation of the conductive read material forming the MR read element. At some point, the degradation of the conductive read material is such that the MR read element no longer allows data to be read from the disk. However, increasing the bias current increases the sensitivity of the MR read element. Accordingly, the selection of bias current is a tradeoff between increased sensitivity and decreased life.
Another factor that contributes to the failure of the MR read element is the average temperature at which the MR read element operates. The operating temperature of the head is referred to as head ambient temperature. In general, increased head ambient temperature decreases the operational life of the MR read element. The head ambient temperature is typically a function of drive ambient temperature and head self-heating. Often, the drive ambient temperature is significantly greater than the drive ambient temperature for which the drive was designed.
In particular, when a hard disk drive is located in a computer, the head ambient temperature is indirectly controlled by various means such as the use of internal fans. Also, in the past, computers were most frequently used in temperature-controlled environments such as offices. However, modern hard disk drives are often included in devices (e.g., DVR's, iPODs, camcorders, etc.) that do not have internal fans and which are placed in environments (e.g., in living rooms, in automobiles, outdoors, etc.) where the temperature is not always controlled. The resulting increased head ambient temperature can significantly decrease the operational life of the MR read element.
Given that a properly functioning MR read element is important to the proper operation of the hard disk drive, a need exists for systems and methods for increasing the operational life of the MR read element, particularly in the context of the increased head ambient temperatures to which modern MR read elements are exposed.